This invention relates to a method of overlaying a stainless steel material for decorative articles and ornaments with an alloy of Au, Pt, and/or Pd bases.
The present inventor has invented a method of the above-mentioned kind, and filed U.S. patent application Ser. No. 150,190 of May 15, 1980, now U.S. Pat. No. 4,309,461 in which there is described a method of overlaying an austenite stainless steel material for decorative articles and ornaments with an alloy of Au, Pt, and/or Pd bases, which comprises plating selected surfaces of the steel material with the constituents of said alloy in any desired order, and one at a time in a plurality of successive layers, and with each layer being of a thickness and volume which corresponds to the constituent ratios of the alloy of a desired purity and dimension, and heating the layers to a temperature sufficient to cause them to liquid phase alloy.
It is now found by him that the alloy of Au, Pt, and/or Pd bases which is overlaid on an ingot stainless steel material for fabricating decorative articles and ornaments such as spectacle frames, watch casings, and watch bracelets by the aforementioned method, does not sometimes present the colour it originally shall have, when the steel material overlaid with the alloy is subjected to a temperature which causes it to liquid phase alloy, viz., a temperature higher than 800.degree. C. This is because that when an alloy of the aforementioned kind is heated to a temperature higher than 800.degree. C., its diffusion into the stainless steel occurs, while constituents of stainless steel such as Fe, Cr, Ni and others which are activated by Au, Pd and/or Pt under an elevated temperature come up into the alloy, too. Their diffusion itself is advantageous for the firm diffusion bonding between the stainless steel matrix and the overlaid precious metal alloy, but it disadvantageously discolors said alloy. Annealing is often required for a stainless steel material either of austenite or ferrite to have its work hardening lessened or released. Unless annealing is made in case of stainless steel matrices overlaid by a precious metal alloy, the alloy shall come off from the matrices when they are subjected to a bending test, because of the hardness of the matrices. If mild stainless steel materials which do not require annealing, are employed, they shall be very weak against sweat. Said annealing which is held at a temperature higher than 800.degree. C. in case of austenite, ferrite or martensite stainless steel for increasing their workability is, however, accompanied also with the diffusion of Fe, Cr, Ni and other contents of stainless steel material into an alloy of Au, Pt and/or Pd bases, which diffusion discolors said alloy.